On Thursday, a monumental decision will be made by the people of the U.K. that could have worldwide implications.
You may have seen the word "Brexit" appear on news channels and social media this week – it's a catchy word combining "British" and "Exit" (which, by the way, is called a portmanteau.)
Brexit describes a United Kingdom referendum, where British citizens vote on whether the U.K. should remain a member of the European Union – or leave.
Here's a look at the implications:
What is the European Union?
The E.U. is a union of 28 European states that was formed in 1953 to bring economic and political stability to a continent ravaged by two world wars – allowing people free movement between countries that are members, as well as tariff-free trade.
It represents 508 million people, and is the world's largest economy in both trading volume and combined nominal GDP, according to the European Commission.
Why is the U.K. voting on this?
Before the 2015 General Election, Prime Minister David Cameron promised people who voted for the Conservative Party that he would hold a referendum on European Union membership if he won, as reported by the BBC.
He did this amid growing dissent from some of his fellow Conservative politicians, and to appease voters who were considering voting for the right-wing populist U.K. Independence Party (UKIP) – which has for years been calling for Brexit, and is considered more conservative than the Conservative Party.
What are the arguments for leaving?
A dominant theme about the "Leave" campaign is immigration. The European Union allows Visa-free movement between the 28 member states. Because of its strong economy and quality of life, the U.K. is a popular destination for economic migrants.
This, they argue, puts a strain on public services and housing availability, and allows security risks into the country (even though unlike other member states, the U.K. still retains control of its border). They are calling for a stricter immigration quota in the event the U.K. leaves the European Union.
The Leave campaign also argues the E.U. is a bloated and bureaucratic political entity, and laws handed down from Brussels have been a point of criticism – prompting calls for the U.K. to "take back control" of its sovereignty.
Each member state elects Members of European Parliament (MEP), but participation in elections is low and they are not seen as being particularly effective or representative – mainly because they are part of just one of several decision-making institutions within the E.U.
What are the arguments for staying in?
Despite claims of it being expensive, the "Remain" campaign has argued that the U.K. benefits enormously from being part of a common market, allowing free movement of goods, capital, services and people. Full Fact notes that 44 percent of U.K. exports go to the E.U.
There have been many warnings from prominent institutions including the International Monetary Fund (IMF), the Bank of England, and the British Treasury that the U.K. and European economy will be plunged into turmoil in the event of a "Leave" vote.
It's not just businesses and the economy that benefit from E.U. membership. The free trade and movement agreement keeps the cost of goods down, and means Britons don't need a Visa to travel to other E.U. countries on vacation.
The European Union has also been responsible for some key legislation during its existence – limiting carbon emissions, preventing worker exploitation, and controlling pesticides to list a few.
Both sides have been accused of fear-mongering – "Remain" about the effects on the economy, and "Leave" about the impact of immigrants – while the level of discourse has at times degenerated to the "post-fact" level, the Washington Post reports.
With Scotland, Northern Ireland and Wales are broadly in favor of "Remain," much of the battle has been fought in England, and the debate has in turn given rise to more extreme elements of English nationalism.
UKIP leader Nigel Farage was roundly criticized by opponents and even supporters of the Leave campaign for this billboard, playing on the fears of Syrian refugees fleeing oppression.
Perhaps the lowest point of the campaign came last week, when a member of Parliament and Remain supporter Jo Cox was shot and killed outside her office by a man who later gave his name in court as "Death to traitors, Freedom for Britain," as reported by the Mirror.
Effect on U.S.
A British exit from the European Union won't affect U.S.-U.K. relations on a diplomatic level, CNN reports, but the U.S. is keen to have the U.K. stay part of the European Union – it's a powerful ally for America when it comes to foreign policy.
The main impact could be an economic one. A Leave vote on Thursday is likely to send stock markets plunging, and Federal Reserve chair Janet Yellen said recently the vote "could have consequences for economic and financial conditions in global financial markets. If it does so, it could have consequences in turn for the U.S. economic outlook."
Yellen said a possible Brexit was a factor in the Federal Reserve's decision not to raise interest rates in June.
Who will win?
The Leave supporters had opened up a bit of a lead as of last week. But the death of Jo Cox and concerns about the impact on household incomes has galvanized Remain support, to the point where polls show it's now around 50-50, according to the Independent.